The present invention is directed generally to a coal storage hopper for feeding coal into a conveying mechanism, and more particularly to an apparatus within a storage hopper for effectively and uniformly feeding moisture-bearing coal particles onto a conveying mechanism under the hopper. This invention was made as a result of a contract with the United States Department of Energy.
The coal feeding and distribution systems used for feeding particulate (finely crushed) coal into various combustion systems are becoming of increasing importance since the sophisticated combustors utilizing particulate coal require a uniform and continuous supply of crushed coal to maintain a desired level of combustion efficiency, effective sulfur capture, minimal tube corrosion, etc. Some problems attendant with the coal distribution systems have been found to be due to the presence of moisture in or on the surface of the coal particles. Crushed coal with up to about 5-6 wt.% surface moisture can be fed from most hopper systems onto a conveyer mechanism without encountering much difficulty. However, with surface moisture greater than about 6 wt.% plugging problems occur in the hopper due to the tendency of the coal to agglomerate and form bridges in the hopper which impair or reduce the efficiency of the coal feeding mechanism.
The utilization of standard hopper designs have not been found to be adequate for maintaining a uniform rate of coal flow with coal containing greater than about 6 wt.% moisture. Efforts to overcome this problem include drying the coal to less than 6 wt.% moisture prior to feeding the coal into the hopper. With the coal dried to less than 6 wt.% moisture content, the coal can be delivered from the hopper onto the conveying mechanism without any plugging problems. But drying the coal is considerably expensive and requires a relatively significant capital investment as well as continuous maintenance and operating costs. Various attempts to modify the hopper systems by changing the shape thereof or by adding a lubricant coating to the hopper, etc. have not significantly improved the feeding characteristics. Additional efforts included the use of push rods in the hopper for breaking up of the coal agglomerates and bridges. These efforts for improving coal feeding have not proved to be as successful as desired for effecting the required uniform feed of the coal from the hopper onto the conveying mechanism.